This invention relates to an electrical switch comprising, a plunger adapted to receive an external axial force thereto and moveable along its axial direction, at least one moveable piece extending substantially normally to the plunger and having at least one moveable contact securely fixed to an end of the moveable piece, a fixed contact securely fixed to a fixed member opposite to the moveable contact, a compression spring means engaged between an intermediate portion of the plunger and an intermediate portion of the movable piece in such a manner that the movable piece may be driven along the axial direction of the plunger through a toggle action of the compression spring means as the plunger is actuated along its axial direction.
An electrical switch of this type may be built in various forms. For instance, the switch may comprise more than one moveable piece and the number of moveable contacts associated therewith may be likewise arbitrarily selected according to the particular needs.
Also more than one fixed contact may be provided and some of them may be normally closed contacts while others may be normally open contacts. Furthermore, the plunger may be provided with a detent mechanism so that the plunger may be held by itself in either one of two or three possible positions, and it is also possible to do away with such a detent mechanism so that the plunger may be in a first position when no force is applied thereto and may move to a second position only when an axial force is applied thereto.
Moreover, the actuation of the plunger may be performed in various forms. It may be adapted to be pushed manually either directly or by way of a lever or other force transmitting means, or, alternatively, it may be adapted to be actuated by another member, for instance, in the form of a limit switch.
In such an electrical switch, particularly when it is connected to an inductive load, sparks are often generated between contacts as they are disengaged and the heat arising from the sparks are often intense enough to melt the contacts. And the pressure acting between the contacts for ensuring low electric resistivity between them often promotes adhesion between the contacts in much the same way as in electric welding.
When this occurs, because the spring force which may be provided for the mechanical switching action of the electrical switch is not enough to disengage the thus mutually welded contacts, and the electrical switch with such mutually welded contacts become totally unusable.
It is known that contacts tend to be progressively degraded as they are used under severe conditions over an extended time period and become more prone to such mutual welding. And the durability of an electrical switch is often determined by this factor.
Furthermore, in an electrical switch of this type, a fault in the compression spring means may render the whole electrical switch unworkable and may cause an extreme inconvenience should such a failure occur when it is strongly necessary to connect or disconnect a certain electric circuit.